Composite material with polyamide particles

ABSTRACT

Pre-impregnated composite material (prepreg) is provided that can be cured/molded to form composite parts having high compression strength under hot and wet conditions, as well as, high damage tolerance and interlaminar fracture toughness. The matrix resin includes a thermoplastic particle component that includes polyamide particles which are composed of the polymeric condensation product of a methyl derivative of bis(4-aminocyclohexyl)methane and an aliphatic dicarboxylic acid.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to pre-impregnated compositematerial (prepreg) that is used in making high performance compositeparts. More particularly, the invention is directed to providing prepregthat may be cured/molded to form composite parts having high compressionstrength under hot and wet conditions, as well as, high damage toleranceand interlaminar fracture toughness.

2. Description of Related Art

Composite materials are typically composed of a resin matrix andreinforcing fibers as the two primary constituents. Composite materialsare often required to perform in demanding environments, such as in thefield of aerospace where the physical limits and characteristics of thecomposite part is of critical importance.

Pre-impregnated composite material (prepreg) is used widely in themanufacture of composite parts. Prepreg is a combination that typicallyincludes uncured resin and fiber reinforcement, which is in a form thatis ready for molding and curing into the final composite part. Bypre-impregnating the fiber reinforcement with resin, the manufacturercan carefully control the amount and location of resin that isimpregnated into the fiber network and ensure that the resin isdistributed in the network as desired. It is well known that therelative amount of fibers and resin in a composite part and thedistribution of resin within the fiber network have a large affect onthe structural properties of the part. Prepreg is a preferred materialfor use in manufacturing load-bearing or primary structural parts andparticularly aerospace primary structural parts, such as wings,fuselages, bulkheads and control surfaces. It is important that theseparts have sufficient strength, damage tolerance and other requirementsthat are routinely established for such parts.

The fiber reinforcements that are commonly used in aerospace prepreg aremultidirectional woven fabrics or unidirectional tape that containsfibers extending parallel to each other. The fibers are typically in theform of a bundle of numerous individual fibers or filaments that isreferred to as a “tow”. The fibers or tows can also be chopped andrandomly oriented in the resin to form a non-woven mat. These variousfiber reinforcement configurations are combined with a carefullycontrolled amount of uncured resin. The resulting prepreg is typicallyplaced between protective layers and rolled up for storage or transportto the manufacturing facility.

Prepreg may also be in the form of short segments of choppedunidirectional tape that are randomly oriented to form a non-woven matof chopped unidirectional tape. This type of prepreg is referred to as a“quasi-isotropic chopped” prepreg. Quasi-isotropic chopped prepreg issimilar to the more traditional non-woven fiber mat prepreg, except thatshort lengths of chopped unidirectional tape (chips) are randomlyoriented in the mat rather than chopped fibers.

The compression strength of a cured composite material is largelydictated by the individual properties of the reinforcing fiber andmatrix resin, as well as the interaction between these two components.In addition, the fiber-resin volume ratio is an important factor. Thecompression strength of a composite part is typically measured at roomtemperature under dry conditions. However, the compression strength isalso routinely measured at elevated temperature (180° F.) under wetconditions. Many parts exhibit a significant drop in compressionstrength under such hot and wet conditions.

In many aerospace applications, it is desirable that the composite partexhibit high compression strength under both room temperature/dryconditions and hot/wet conditions. However, attempts to keep compressionstrength constant under hotter/wetter conditions often result innegative effects on other desirable properties, such as damage toleranceand interlaminar fracture toughness.

Selecting higher modulus resins can be an effective way to increase thecompression strength of a composite. However, this can result in atendency to reduce damage tolerance, which is typically measured by adecrease in compressive properties, such as compression after impact(CAI) strength. Accordingly, it is very difficult to achieve asimultaneous increase in both the compression strength and damagetolerance.

Multiple layers of prepreg are commonly used to form composite partsthat have a laminated structure. Delamination of such composite parts isan important failure mode. Delamination occurs when two layers debondfrom each other. Important design limiting factors include both theenergy needed to initiate a delamination and the energy needed topropagate it. The initiation and growth of a delamination is oftendetermined by examining Mode I and Mode II fracture toughness. Fracturetoughness is usually measured using composite materials that have aunidirectional fiber orientation. The interlaminar fracture toughness ofa composite material is quantified using the G1c (Double CantileverBeam) and G2c (End Notch Flex) tests. In Mode I, the pre-crackedlaminate failure is governed by peel forces and in Mode II the crack ispropagated by shear forces.

A simple way to increase interlaminar fracture toughness has been toincrease the ductility of the matrix resin by introducing thermoplasticsheets as interleaves between layers of prepreg. However, this approachtends to yield stiff, tack-free materials that are difficult to use.Another approach has been to include a toughened resin interlayer ofabout 20 to 50 microns thickness between fiber layers. The toughenedresin includes thermoplastic particles. Polyamides have been used assuch thermoplastic particles.

Although existing prepregs are well suited for their intended use inproviding composite parts that are strong and damage tolerant, therestill is a continuing need to provide prepreg that may be used to makecomposite parts that have even higher levels of compression strengthunder hot and wet conditions, high damage tolerance (CAI) and highinterlaminar fracture toughness (G1c and G2c).

SUMMARY OF THE INVENTION

In accordance with the present invention, pre-impregnated compositematerial (prepreg) is provided that can be molded to form compositeparts that have high levels of strength, damage tolerance andinterlaminar fracture toughness. This is achieved without causing anysubstantial negative impact upon the physical or chemicalcharacteristics of the uncured prepreg or the cured composite part.

The pre-impregnated composite materials of the present invention arecomposed of reinforcing fibers and a matrix. The matrix includes a resincomponent made up of difunctional epoxy resin in combination with one ormore multifunctional epoxy resins. The matrix further includes athermoplastic particle component, a thermoplastic toughening agent and acuring agent. As a feature of the present invention, the thermoplasticparticle component is composed of thermoplastic particles that comprisea polyamide which is the polymeric condensation product of a methylderivative of bis(4-aminocyclohexyl)methane and 1,10-decane dicarboxylicacid.

The present invention also covers methods for making the prepreg andmethods for molding the prepreg into a wide variety of composite parts.The invention also covers the composite parts that are made using theimproved prepreg.

It has been found that the use of matrix containing thermoplasticparticles that are composed of a polyamide condensation product, as setforth above, results in the formation of prepreg that may be molded toform composite parts that have high levels of strength, damage toleranceand interlaminar fracture toughness in comparison to conventionalsystems.

The above described and many other features and attendant advantages ofthe present invention will become better understood by reference to thefollowing detailed description.

DETAILED DESCRIPTION OF THE INVENTION

The pre-impregnated composite materials (prepreg) of the presentinvention may be used as a replacement for existing prepreg that isbeing used to form composite parts in the aerospace industry and in anyother application where high structural strength and damage tolerance isrequired. The invention involves substituting the resin formulations ofthe present invention in place of existing resins that are being used tomake prepreg. Accordingly, the resin formulations of the presentinvention are suitable for use in any of the conventional prepregmanufacturing and curing processes.

The pre-impregnated composite materials of the present invention arecomposed of reinforcing fibers and an uncured matrix. The reinforcingfibers can be any of the conventional fiber configurations that are usedin the prepreg industry. The matrix includes a conventional resincomponent that is made up of difunctional epoxy resin in combinationwith at least one multifunctional aromatic epoxy resin with afunctionality greater than two. The matrix further includes athermoplastic particle component, a thermoplastic toughening agent and acuring agent. A feature of the present invention is that thethermoplastic particle component is composed of thermoplastic particlesthat comprise a polyamide which is the polymeric condensation product ofa methyl derivative of bis(4-aminocyclohexyl)methane and decanedicarboxylic acid, which is also known as 1,12-dodecanedioic acid.

It was discovered that the use of polyamide particles in accordance withthe present invention provided composite materials with unexpectedlyhigh damage tolerance (CAI of over 60), as well as high compressivestrength and interlaminar toughness.

The difunctional epoxy resin used to form the resin component of thematrix may be any suitable difunctional epoxy resin. It will beunderstood that this includes any suitable epoxy resins having two epoxyfunctional groups. The difunctional epoxy resin may be saturated,unsaturated, cycloaliphatic, alicyclic or heterocyclic.

Difunctional epoxy resins, by way of example, include those based on:diglycidyl ether of Bisphenol F, Bisphenol A (optionally brominated),glycidyl ethers of phenol-aldelyde adducts, glycidyl ethers of aliphaticdiols, diglycidyl ether, diethylene glycol diglycidyl ether, Epikote,Epon, aromatic epoxy resins, epoxidised olefins, brominated resins,aromatic glycidyl amines, heterocyclic glycidyl imidines and amides,glycidyl ethers, fluorinated epoxy resins, or any combination thereof.The difunctional epoxy resin is preferably selected from diglycidylether of Bisphenol F, diglycidyl ether of Bisphenol A, diglycidyldihydroxy naphthalene, or any combination thereof. Most preferred isdiglycidyl ether of Bisphenol F. Diglycidyl ether of Bisphenol F isavailable commercially from Huntsman Advanced Materials (Brewster, N.Y.)under the trade names Araldite GY281 and GY285 and from Ciba-Geigy(location) under the trade name LY9703. A difunctional epoxy resin maybe used alone or in any suitable combination with other difunctionalepoxies.

The difunctional epoxy resin is present in the range 10 wt % to 40 wt %of the matrix. Preferably, the difunctional epoxy resin is present inthe range 15 wt % to 35 wt %. More preferably, the difunctional epoxyresin is present in the range 20 wt % to 25 wt %.

The second component of the matrix is one or more epoxy resins with afunctionality that is greater than two. Preferred multifunctional epoxyresins are those that are trifunctional or tetrafunctional. Themultifunctional epoxy resin may be a combination of trifunctional andmultifunctional epoxies. The multifunctional epoxy resins may besaturated, unsaturated, cylcoaliphatic, alicyclic or heterocyclic.

Suitable multifunctional epoxy resins, by way of example, include thosebased upon: phenol and cresol epoxy novolacs, glycidyl ethers ofphenol-aldelyde adducts; glycidyl ethers of dialiphatic diols;diglycidyl ether; diethylene glycol diglycidyl ether; aromatic epoxyresins; dialiphatic triglycidyl ethers, aliphatic polyglycidyl ethers;epoxidised olefins; brominated resins; aromatic glycidyl amines;heterocyclic glycidyl imidines and amides; glycidyl ethers; fluorinatedepoxy resins or any combination thereof.

A trifunctional epoxy resin will be understood as having the three epoxygroups substituted either directly or indirectly in a para or metaorientation on the phenyl ring in the backbone of the compound. Atetrafunctional epoxy resin will be understood as having the four epoxygroups substituted either directly or indirectly in a meta or paraorientation on the phenyl ring in the backbone of the compound.

The phenyl ring may additionally be substituted with other suitablenon-epoxy substituent groups. Suitable substituent groups, by way ofexample, include hydrogen, hydroxyl, alkyl, alkenyl, alkynyl, alkoxyl,aryl, aryloxyl, aralkyloxyl, aralkyl, halo, nitro, or cyano radicals.Suitable non-epoxy substituent groups may be bonded to the phenyl ringat the para or ortho positions, or bonded at a meta position notoccupied by an epoxy group. Suitable tetrafunctional epoxy resinsinclude N,N,N′,N′-tetraglycidyl-m-xylenediamine (available commerciallyfrom Mitsubishi Gas Chemical Company (Chiyoda-Ku, Tokyo, Japan) underthe name Tetrad-X), and Erisys GA-240 (from CVC Chemicals, Morrestown,N.J.). Suitable trifunctional epoxy resins, by way of example, includethose based upon: phenol and cresol epoxy novolacs; glycidyl ethers ofphenol-aldelyde adducts; aromatic epoxy resins; dialiphatic triglycidylethers; aliphatic polyglycidyl ethers; epoxidised olefins; brominatedresins, aromatic glycidyl amines and glycidyl ethers; heterocyclicglycidyl imidines and amides; glycidyl ethers; fluorinated epoxy resinsor any combination thereof.

An exemplary trifunctional epoxy resin is triglycidyl meta-aminophenol.Triglycidyl meta-aminophenol is available commercially from HuntsmanAdvanced Materials (Monthey, Switzerland) under the trade name AralditeMY0600 and from Sumitomo Chemical Co. (Osaka, Japan) under the tradename ELM-120. Another exemplary trifunctional epoxy resin is triglycidylpara-aminophenol. Triglycidyl para-aminophenol is available commerciallyfrom Huntsman Advanced Materials (Monthey, Switzerland) under the tradename Araldite MY0510.

Additional examples of suitable multifunctional epoxy resin include, byway of example, N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl methane(TGDDM available commercially as Araldite MY720 and MY721 from HuntsmanAdvanced Materials (Monthey, Switzerland), or ELM 434 from Sumitomo),triglycidyl ether of para aminophenol (available commercially asAraldite MY 0500 or MY 0510 from Huntsman Advanced Materials),dicyclopentadiene based epoxy resins such as Tactix 556 (availablecommercially from Huntsman Advanced Materials), tris-(hydroxyl phenyl),and methane-based epoxy resin such as Tactix 742 (available commerciallyfrom Huntsman Advanced Materials). Other suitable multifunctional epoxyresins include DEN 438 (from Dow Chemicals, Midland, Mich.), DEN 439(from Dow Chemicals), Araldite ECN 1273 (from Huntsman AdvancedMaterials), and Araldite ECN 1299 (from Huntsman Advanced Materials).

Preferably, the epoxy resin(s) with a functionality that is greater than2 will be present in the range 15 wt % to 35 wt % of the matrix. Morepreferably, the difunctional epoxy resin is present in the range of 20wt % to 25 wt % of the total weight of the matrix. The total resincomponent content resin (difunctional+trifunctional+tetrafunctional)will be in the range 40 wt % to 60 wt % of the total matrix.

The prepreg matrix in accordance with the present invention alsoincludes a thermoplastic particle component that is composed ofpolyamide particles which are a polymeric condensation product of amethyl derivative of bis(4-aminocyclohexyl)methane and an aliphaticdicarboxylic acid selected from the group consisting of decanedicarboxylic acid and dodecane dicarboxylic acid. Methyl derivatives ofbis(4-aminocyclohexyl)methane, which are referred to herein as the“amine component” are also known as methyl derivatives of4,4′-diaminocyclohexylmethane.

The polyamide particles and the methods for making them are described indetail in U.S. Pat. Nos. 3,936,426 and 5,696,202, the contents of whichare hereby incorporated by reference.

The formula for the amine component of the polymeric condensationproduct is

where R₂ is hydrogen, methyl or ethyl and R₁ is methyl, ethyl orhydrogen wherein at least one of R₁ is methyl or ethyl. A preferredamine component is where both R₁ are methyl and both R₂ are hydrogen.

The preferred polyamide particles are made from the polymericcondensation product of 3,3′-dimethyl-bis(4-aminocyclohexyl)methane (R₁both are methyl and R₂ both are hydrogen) and 1,10-decane dicarboxylicacid. The preferred polyamide particles are made by combining, in aheated receiving vessel, 13,800 grams of 1,10-decane dicarboxylic acidand 12,870 grams of 3,3′-dimethyl-bis(4-aminocyclohexyl)methane with 30grams of 50% aqueous phosphoric acid, 150 grams benzoic acid and 101grams of water. The mixture is stirred in a pressure autoclave untilhomogeneous. After a compression, decompression and degassing phase, thepolyamide condensation product is pressed out as a strand, passed undercold water and granulated to form polyamide particles. Preferredpolyamide particles can also be made from GRILAMID TR90, which iscommercially available from EMS-Chime (Sumter, S.C.). GRILAMID TR90 isthe polymeric condensation product of3,3′-dimethyl-bis(4-aminocyclohexyl)methane and 1,10-decane dicarboxylicacid.

The formula for the monomeric unit of the preferred polymericcondensation product may be represented as follows:

The molecular number of the preferred polymeric condensation productwill range from 14,000 to 20,000 with a molecular numbers of about17,000 being particularly preferred.

The polyamide particles should have particle sizes of below 100 microns.It is preferred that the particles range in size from 5 to 60 micronsand more preferably from 10 to 30 microns. It is preferred that theaverage particle size is from 15 to 25 microns. The particles may beregular or irregular in shape. For example, the particles may besubstantially spherical or they can be particles with a jagged shape.

The thermoplastic particle component is present in the range 5 wt % to20 wt % of the matrix. Preferably, there will be from 5 to 15 wt %thermoplastic particles. At least 40 wt % of the thermoplastic particlesin the thermoplastic particle component should be composed of polyamidecondensation product in accordance with the present invention, asdescribed above. Preferably, the amount of polyamide condensationproduct particles in the thermoplastic component will be over 50 wt %with amounts of such polyamide particles above 95 wt % beingparticularly preferred. Up to 60 wt % of other thermoplastic particles,such as other types of polyamide particles, may be included in thethermoplastic component, if desired. For example, see U.S. Pat. No.7,754,322, the contents of which is hereby incorporated by reference,for other types of polyamide particles that can be used. Preferably, theamount of other types of polyamide particles will be below 50 wt % ofthe thermoplastic component. Particularly preferred are thermoplasticcomponents that include amounts of other polyamide particles of lessthan 5 wt %.

The individual polyamide particles made from the condensation product,as described above, should contain at least 90 wt % of the condensationproduct. Preferably, the polyamide particles should contain at least 95wt % of the condensation product and more preferably at least 98 wt % ofthe condensation product.

The prepreg matrix resin includes at least one curing agent. Suitablecuring agents are those which facilitate the curing of theepoxy-functional compounds of the invention and, particularly,facilitate the ring opening polymerization of such epoxy compounds. In aparticularly preferred embodiment, such curing agents include thosecompounds which polymerize with the epoxy-functional compound orcompounds, in the ring opening polymerization thereof. Two or more suchcuring agents may be used in combination.

Suitable curing agents include anhydrides, particularly polycarboxylicanhydrides, such as nadic anhydride (NA), methylnadic anhydride(MNA—available from Aldrich), phthalic anhydride, tetrahydrophthalicanhydride, hexahydrophthalic anhydride (HHPA—available from Anhydridesand Chemicals Inc., Newark, N.J.), methyltetrahydrophthalic anhydride(MTHPA—available from Anhydrides and Chemicals Inc.),methylhexahydrophthalic anhydride (MHHPA—available from Anhydrides andChemicals Inc.), endomethylenetetrahydrophthalic anhydride,hexachloroendomethylene-tetrahydrophthalic anhydride (ChlorenticAnhydride—available from Velsicol Chemical Corporation, Rosemont, Ill.),trimellitic anhydride, pyromellitic dianhydride, maleic anhydride(MA—available from Aldrich), succinic anhydride (SA), nonenylsuccinicanhydride, dodecenylsuccinic anhydride (DDSA—available from Anhydridesand Chemicals Inc.), polysebacic polyanhydride, and polyazelaicpolyanhydride.

Further suitable curing agents are the amines, including aromaticamines, e.g., 1,3-diaminobenzene, 1,4-diaminobenzene,4,4′-diamino-diphenylmethane, and the polyaminosulphones, such as4,4′-diaminodiphenyl sulphone (4,4′-DDS—available from Huntsman),4-aminophenyl sulphone, and 3,3′-diaminodiphenyl sulphone (3,3′-DDS).Also, suitable curing agents may include polyols, such as ethyleneglycol (EG—available from Aldrich), poly(propylene glycol), andpolyvinyl alcohol); and the phenol-formaldehyde resins, such as thephenol-formaldehyde resin having an average molecular weight of about550-650, the p-t-butylphenol-formaldehyde resin having an averagemolecular weight of about 600-700, and the p-n-octylphenol-formaldehyderesin, having an average molecular weight of about 1200-1400, thesebeing available as HRJ 2210, HRJ-2255, and SP-1068, respectively, fromSchenectady Chemicals, Inc., Schenectady, N.Y.). Further as tophenol-formaldehyde resins, a combination of CTU guanamine, andphenol-formaldehyde resin having a molecular weight of 398, which iscommercially available as CG-125 from Ajinomoto USA Inc. (Teaneck,N.J.), is also suitable.

Different commercially available compositions may be used as curingagents in the present invention. One such composition is AH-154, adicyanodiamide type formulation, available from Ajinomoto USA Inc.Others which are suitable include Ancamide 400, which is a mixture ofpolyamide, diethyltriamine, and triethylenetetraamine, Ancamide 506,which is a mixture of amidoamine, imidazoline, andtetraethylenepentaamine, and Ancamide 1284, which is a mixture of4,4′-methylenedianiline and 1,3-benzenediamine; these formulations areavailable from Pacific Anchor Chemical, Performance Chemical Division,Air Products and Chemicals, Inc., Allentown, Pa.

Additional suitable curing agents include imidazole(1,3-diaza-2,4-cyclopentadiene) available from Sigma Aldrich (St. Louis,Mo.), 2-ethyl-4-methylimidazole available from Sigma Aldrich, and borontrifluoride amine complexes, such as Anchor 1170, available from AirProducts & Chemicals, Inc.

Still additional suitable curing agents include3,9-bis(3-aminopropyl-2,4,8,10-tetroxaspiro[5.5]undecane, which iscommercially available as ATU, from Ajinomoto USA Inc., as well asaliphatic dihydrazide, which is commercially available as Ajicure UDH,also from Ajinomoto USA Inc., and mercapto-terminated polysulphide,which is commercially available as LP540, from Morton International,Inc., Chicago, Ill.

The curing agent(s) is selected so that it provides curing of the matrixat suitable temperatures. The amount of curing agent required to provideadequate curing of the matrix will vary depending upon a number offactors including the type of resin being cured, the desired curingtemperature and curing time. Curing agents typically may also includecyanoguanidine, aromatic and aliphatic amines, acid anhydrides, LewisAcids, substituted ureas, imidazoles and hydrazines. The particularamount of curing agent required for each particular situation may bedetermined by well-established routine experimentation.

Exemplary preferred curing agents include 4,4′-diaminodiphenyl sulphone(4,4′-DDS) and 3,3′-diaminodiphenyl sulphone (3,3′-DDS), bothcommercially available from Huntsman.

The curing agent is present in an amount that ranges from 5 wt % to 45wt % of the uncured matrix. Preferably, the curing agent is present inan amount that ranges from 10 wt % to 30 wt %. More preferably, thecuring agent is present in the range 15 wt % to 25 wt % of the uncuredmatrix. Most preferred is a matrix that contains from 18 wt % to 22 wt %curing agent based on the total weight of the matrix.

3,3′-DDS is a particularly preferred curing agent. It is preferably usedas the sole curing agent in an amount ranging from 18 wt % to 22 wt %.Small amounts (less than 2 wt %) of other curatives, such as 4,4′-DDS,may be included, if desired.

The matrix of the present invention also preferably includes athermoplastic toughening agent. Any suitable thermoplastic polymers maybe used as the toughening agent. Typically, the thermoplastic polymer isadded to the resin mix as particles that are dissolved in the resinmixture by heating prior to addition of the curing agent. Once thethermoplastic agent is substantially dissolved in the hot matrix resinprecursor (i.e. the blend of epoxy resins), the precursor is cooled andthe remaining ingredients (curing agent and insoluble thermoplasticparticles) are added.

Exemplary thermoplastic toughening agents/particles include any of thefollowing thermoplastics, either alone or in combination: polysulphones,polyethersulfonones, high performance hydrocarbon polymers, elastomers,and segmented elastomers.

The toughening agent is present in the range 10 wt % to 40 wt % of theuncured resin matrix. Preferably, the toughening agent is present in therange 15 wt % to 30 wt %. More preferably, the toughening agent ispresent in the range 20 wt % to 25 wt %. A suitable toughening agent, byway of example, is particulate PES sold under the trade name Sumikaexcel5003P, which is commercially available from Sumitomo Chemicals.Alternatives to 5003P are Solvay polyethersulphone 105RP, or thenon-hydroxyl terminated grades such as Solvay 1054P. Densified PESparticles may be used as the toughening agent. The form of the PES isnot particularly important since the PES is dissolved during formationof the resin. Densified PES particles can be made in accordance with theteachings of U.S. Pat. No. 4,945,154, the contents of which are herebyincorporated by reference. Densified PES particles are also availablecommercially from Hexcel Corporation (Dublin, Calif.) under the tradename HRI-1. The average particle size of the toughening agent should beless than 100 microns to promote and insure complete dissolution of thePES in the matrix.

The matrix may also include additional ingredients, such as performanceenhancing or modifying agents and additional thermoplastic polymersprovided they do not adversely affect the tack and outlife of theprepreg or the strength and damage tolerance of the cured compositepart. The performance enhancing or modifying agents, for example, may beselected from flexibilizers, non-particulate toughening agents,accelerators, core shell rubbers, flame retardants, wetting agents,pigments/dyes, UV absorbers, anti-fungal compounds, fillers, conductingparticles, and viscosity modifiers.

Suitable accelerators are any of the urone compounds that have beencommonly used. Specific examples of accelerators, which may be usedalone or in combination, include N,N-dimethyl, N′-3,4-dichlorophenylurea (Diuron), N′-3-chlorophenyl urea (Monuron), and preferablyN,N-(4-methyl-m-phenylene bis[N′,N′-dimethylurea] (e.g. Dyhard UR500available from Degussa).

Suitable fillers include, by way of example, any of the following eitheralone or in combination: silicas, aluminas, titania, glass, calciumcarbonate and calcium oxide.

Suitable conducting particles, by way of example, include any of thefollowing either alone or in combination: silver, gold, copper,aluminum, nickel, conducting grades of carbon, buckminsterfullerene,carbon nanotubes and carbon nanofibres. Metal-coated fillers may also beused, for example nickel coated carbon particles and silver coatedcopper particles.

The matrix may include small amounts (less than 5 wt %) of an additionalnon-epoxy thermosetting polymeric resin. Once cured, a thermoset resinis not suitable for melting and remolding. Suitable non-epoxy thermosetresin materials for the present invention include, but are not limitedto, resins of phenol formaldehyde, urea-formaldehyde,1,3,5-triazine-2,4,6-triamine (Melamine), bismaleimide, vinyl esterresins, benzoxazine resins, phenolic resins, polyesters, cyanate esterresins, epoxide polymers, or any combination thereof. The thermosetresin is preferably selected from epoxide resins, cyanate ester resins,benzoxazine and phenolic resins. If desired, the matrix may includefurther suitable resins containing phenolic groups, such as resorcinolbased resins, and resins formed by cationic polymerization, such asDCPD—phenol copolymers. Still additional suitable resins aremelamine-formaldehyde resins, and urea-formaldehyde resins.

The resin matrix is made in accordance with standard prepreg matrixprocessing. In general, the various epoxy resins are mixed together atroom temperature to form a resin mix to which the thermoplastictoughening agent is added. This mixture is then heated to about 120° C.for about 1 to 2 hours to dissolve the thermoplastic toughening. Themixture is then cooled down to about 80° C. and the remainder of theingredients (thermoplastic particle component, curing agent and otheradditive, if any) is mixed into the resin to form the final matrix resinthat is impregnated into the fiber reinforcement.

The matrix resin is applied to the fibrous reinforcement in accordancewith any of the known prepreg manufacturing techniques. The fibrousreinforcement may be fully or partially impregnated with the matrixresin. In an alternate embodiment, the matrix resin may be applied tothe fiber fibrous reinforcement as a separate layer, which is proximalto, and in contact with, the fibrous reinforcement, but does notsubstantially impregnate the fibrous reinforcement. The prepreg istypically covered on both sides with a protective film and rolled up forstorage and shipment at temperatures that are typically kept well belowroom temperature to avoid premature curing. Any of the other prepregmanufacturing processes and storage/shipping systems may be used ifdesired.

The fibrous reinforcement of the prepreg may be selected from hybrid ormixed fiber systems that comprise synthetic or natural fibers, or acombination thereof. The fibrous reinforcement may preferably beselected from any suitable material such as fiberglass, carbon or aramid(aromatic polyamide) fibers. The fibrous reinforcement is preferablycarbon fibers.

The fibrous reinforcement may comprise cracked (i.e. stretch-broken) orselectively discontinuous fibers, or continuous fibers. It is envisagedthat use of cracked or selectively discontinuous fibers may facilitatelay-up of the composite material prior to being fully cured, and improveits capability of being shaped. The fibrous reinforcement may be in awoven, non-crimped, non-woven, unidirectional, or multi-axial textilestructure form, such as quasi-isotropic chopped prepreg. The woven formmay be selected from a plain, satin, or twill weave style. Thenon-crimped and multi-axial forms may have a number of plies and fiberorientations. Such styles and forms are well known in the compositereinforcement field, and are commercially available from a number ofcompanies, including Hexcel Reinforcements (Villeurbanne, France).

The prepreg may be in the form of continuous tapes, towpregs, webs, orchopped lengths (chopping and slitting operations may be carried out atany point after impregnation). The prepreg may be an adhesive orsurfacing film and may additionally have embedded carriers in variousforms both woven, knitted, and non-woven. The prepreg may be fully oronly partially impregnated, for example, to facilitate air removalduring curing.

An exemplary preferred matrix resin includes from 20 wt % to 25 wt %Bisphenol-F diglycidyl ether; from 20 wt % to 25 wt %triglycidyl-p-aminophenol (trifunctional epoxy resin); from 17 wt % to22 wt % diaminodiphenylsulphone (primarily 3,3-DDS as a curing agent);from 10 wt % to 15 wt % polyamide particles that are a polymericcondensation product of 3,3′-dimethyl-bis(4-aminocyclohexyl)methane anddodecane dicarboxylic acid; and from 10 wt % to 26 wt % ground densifiedpolyether sulphone as a toughening agent.

The prepreg may be molded using any of the standard techniques used toform composite parts. Typically, one or more layers of prepreg are placein a suitable mold and cured to form the final composite part. Theprepreg of the invention may be fully or partially cured using anysuitable temperature, pressure, and time conditions known in the art.Typically, the prepreg will be cured in an autoclave at temperatures ofbetween 160° C. and 190° C. The composite material may be cured using amethod selected from microwave radiation, electron beam, gammaradiation, or other suitable thermal or non-thermal radiation.

Composite parts made from the improved prepreg of the present inventionwill find application in making articles such as numerous primary andsecondary aerospace structures (wings, fuselages, bulkheads and thelike), but will also be useful in many other high performance compositeapplications including automotive, rail and marine applications wherehigh compressive strength, interlaminar fracture toughness andresistance to impact damage are needed.

In order that the present invention may be more readily understood,reference will now be made to the following background information andexamples of the invention.

Example 1

A preferred exemplary resin formulation in accordance with the presentinvention is set forth in TABLE 1. A matrix resin was prepared by mixingthe epoxy ingredients at room temperature with the polyethersulfone toform a resin blend that was heated to 130° C. for 60 minutes tocompletely dissolve the polyethersulfone. The mixture was cooled to 80°C. and the rest of the ingredients added and mixed in thoroughly.

TABLE 1 Ingredient Amount (Wt %) Bisphenol-F diglycidyl ether (LY9703)22.5 Trifunctional para-glycidyl amine (MY0510) 22.5 Aromatic diaminecuring agent (3,3-DDS) 19.6 Thermoplastic Toughening Agent (HRI-1 23.4polyether sulfone) Polyamide particles (25 microns) that are a 12.0polymeric condensation product of 3,3′-dimethyl-bis(4-aminocyclohexyl)methane and 1,10-decane dicarboxylic acid(GRILAMID TR90)

Exemplary prepreg was prepared by impregnating one or more layers ofunidirectional carbon fibers with the resin formulation of TABLE 1. Theunidirectional carbon fibers (IM7 available from Hexcel Corporation)were used to make a prepreg in which the matrix resin amounted to 35weight percent of the total uncured prepreg weight and the fiber arealweight was 145 grams per square meter (gsm). A variety of prepreg layups were prepared using standard prepreg fabrication procedures. Theprepregs were cured in an autoclave at 180° C. for about 2 hours. Thecured prepregs were then subjected to standard tests to determine theirtolerance to damage (CAI), interlaminar fracture toughness (G1c and G2c)and compressive strength under both room temperature/dry conditions and180° F./wet conditions, as described below.

Compression after Impact (CAI) was determined using a 270 in-lb impactagainst a 4-ply quasi-isotropic laminate. The laminate was cured at 180°C. for 2 hours in the autoclave. The final laminate thickness was about4.5 mm. The consolidation was verified by c-scan. The specimens weremachined, impacted and tested in accordance with Boeing test methodBSS7260 per BMS 8-276. Values are normalized to a nominal cured laminatethickness of 0.18 inches.

G1c and G2c are standard tests that provide a measure of theinterlaminar fracture toughness of the cured laminate. G1c and G2c weredetermined as follows. A 4-ply unidirectional laminate was cured with a3 inch fluoroethylene polymer (FEP) film inserted along one edge, at themid-plane of the layup, perpendicular to the fiber direction to act as acrack starter. The laminate was cured for 2 hours at 180° C., in anautoclave and gave a nominal thickness of 3.8 mm. Consolidation wasverified by C-scan. Both G1c and G2c samples were machined from the samecured laminate. G1c was tested in accordance with Boeing test methodBSS7233 and G2c was tested in accordance with BSS7320. Values for G1cand G2c were not normalized.

The 0° Compressive strength at room temperature under dry conditions wasdetermined according to BS7260. The 0° Compressive strength at 180° F.under wet conditions was also determined according to BSS7260.

Surprisingly, the CAI was determined to be 61.3. Since this is arelatively high and unexpected CAI level, a second sample was retestedto confirm the test result. Upon retesting, the CAI of the laminate wasfound to be 60.1, which is well within expected experimental error. TheCAI of over 60 is very high in comparison to laminates made usingpolyamide tougheners other than TR90. The G1c and G2c values wererelatively high at 2.8 and 8.8, respectively. The 0° compressivestrength was 259 at room temperature under dry conditions, which isrelatively high. The 0° compressive strength remained relative high(189) when measured at 180° C. under wet conditions.

The above example demonstrates that an unexpectedly high damagetolerance (CAI) in combination with high interlaminar fracture toughnessand compressive strength can be achieved when polyamide particles inaccordance with the present invention are used in the matrix.

Comparative Example 1

A comparative prepreg was prepared and cured in the same manner asExample 1. A matrix formulation was used in which the thermoplasticcomponent contained polyamide particles that are available commerciallyfrom Arkema (France) under the trade names Orgasol 1002 and Orgasol3803. Orgasol 1002 is composed of 100% PA6 particles having an averageparticle size of 20 microns. Orgasol 3803 is composed of particles thatare a copolymer of 80% PA12 and 20% PA6 with the mean particle sizebeing from 17 to 24 microns. The prepreg was prepared using the same IM7carbon fiber. The prepreg contained 35% resin by weight and had a fiberareal weight of 145 gsm. The formulation used for the comparativeprepreg is set forth in TABLE 2.

TABLE 2 Ingredient Amount (wt %) Bisphenol-F diglycidyl ether (GY285)17.3 Trifunctional meta-glycidyl amine 26.2 (MY0600)N,N,N′,N′-tetraglycidyl-4,4′- 10.5 diaminodiphenyl methane (MY721) PES(5003P) 15.7 4,4-DDS 20.9 Polyamide 12 Particles (Orgasol 1002) 4.75Polyamide 12 Particles 4.75 (Orgasol 3803)

The cured comparative prepreg was tested in the same manner asExample 1. The CAI was 57.9 and the G1c and G2c were 2.1 and 7.3,respectively. The 0° compressive strength at room temperature was 269.The 0° compressive strength fell to 160 when measured at 180° C. underwet conditions. Use of the polyamide condensation product particles inaccordance with the present invention avoids this substantial drop incompressive strength that occurred under hot and wet conditions.

Example 2

Additional exemplary prepregs were prepared in the same manner asExample 1, except that the fiber reinforcement was IM10. IM10 is aunidirectional carbon fiber material which is also available from HexcelCorporation (Dublin, Calif.). The exemplary matrix formulations are setforth in TABLE 3. The exemplary prepregs included matrix resin in anamount of 35 weight percent of the total uncured prepreg weight and thefiber areal weight of the IM10 fiber was 145 grams per square meter(gsm). SP 10L are PA12 polyamide particles) that are availablecommercially from Toray Industries (Japan).

TABLE 3 2A 2B Ingredient (wt %) (wt %) GY285 17.0 16.6 MY0600 25.7 25.1MY721 10.3 10.1 PES 5003P 18.7 18.7 TR90 (25 microns) 4.75 6.75 SP10L6.25 6.25 3,3-DDS 20.6 20.1

The cured exemplary prepregs were subjected to the same testingprocedures as in Example 1. The results are set forth in TABLE 4.

TABLE 4 2A 2B CAI 57.6 59.2 G1c 2.3 2.2 G2c 12.2 3.0 0° Comp. Strength280 271 (RT/dry) 0° Comp. Strength 187 187 (180° C./wet)

Examples 2A and 2B demonstrate that thermoplastic components whichinclude at least 40 wt % polyamide condensation product particles inaccordance with the present invention provide significant improvement inthe 0° compressive strength as compared to Comparative Example 1. Inorder to obtain the additional benefit of CAI values of 60 and over, itis preferred that at least 95 wt % (preferably 100 percent) of thethermoplastic particles be polyamide condensation particles inaccordance with the present invention as demonstrated in Example 1.

Comparative Examples 2-8

Comparative prepregs (C2 to C8) were prepared in the same manner asExample 2 using IM10 fibers. The formulations for the comparativematrices are set forth in TABLE 5. Rislan PA11 particles are made frompolamide11 and are available commercially from Arkema. The Rislan PA11particles had an average particle size of 20 microns.

TABLE 5 C2 C3 (wt (wt C4 C5 C6 C7 C8 Ingredient %) %) (wt %) (wt %) (wt%) (wt %) (wt %) GY285 17.3 17.3 16.3 16.3 17.0 17.0 17.0 MY0600 26.226.2 24.6 24.6 25.7 25.7 25.7 MY721 10.5 10.5 9.8 9.8 10.3 10.3 10.3 PES15.7 15.7 14.7 14.7 15.4 15.4 15.4 5003P Orgasol 4.75 4.75 4.75 1002Orgasol 4.75 3803 Rilsan 4.75 7.50 7.50 6.25 PA11 SP10L 4.75 7.50 7.504.75 6.25 6.25 3,3-DDS 20.9 20.1 19.6 20.6 20.6 10.3 4,4-DDS 19.6 10.3

The cured prepregs were subjected to the same testing procedures as inExamples 2A and 2B. The results are set forth in TABLE 6.

TABLE 6 C2 C3 C4 C5 C6 C7 C8 CAI 54.9 53.7 55.5 55.2 54.5 48.8 49.3 G1c2.2 2.0 2.3 2.4 2.1 2.2 2.4 G2c 6.3 6.1 12.0 12.0 9.1 6.9 6.6 0° Comp.259 284 256 277 271 263 256 Strength (RT/dry) 0° Comp. 192 195 154 171193 170 169 Strength 180° C./wet)

The comparative examples demonstrate that achieving a high CAI (60 ormore) in combination with a high 0° hot/wet compressive strength (over180) could not be achieved using various combinations of polyamideparticles that did not include the polyamide condensation product inaccordance with the present invention.

Comparative Example 9

A comparative prepreg (C9) was made in the same manner as Example 1,except that thermoplastic particle component included a blend of SP 10Lparticles and GRILAMIDE TR60 particles in place of GRILAMIDE TR90particles. GRILAMIDE TR60 is similar to TR90, except that TR60 has anaromatic polymer backbone and TR90 has an aliphatic polymer backbone.The resin formulation for this comparative prepreg is set forth in TABLE8.

TABLE 8 C9-Ingredient Amount (Wt %) Bisphenol-F diglycidyl ether(TY9703) 22.5 Trifunctional para-glycidyl amine (MY0510) 22.5 Aromaticdiamine curing agent (3,3-DDS) 19.6 Thermoplastic Toughening Agent (HR123.4 Densified polyether sulfone) Polyamide particles - GRILAMID TR607.9 (25 microns) Polyamide particles - Sp10L 4.1

The cured comparative prepreg (C9) was subjected to the same testing asin Examples 1. The CAI was only 54.9, which is relatively low incomparison to Examples 1, 2A and 2B. The G1c and G2c values wereacceptable at 2.1 and 8.0, respectively. The 0° compressive strength wasan acceptable 255 at room temperature under dry conditions, but droppedto 171 when measured at 180° C. under wet conditions. The hot/wetcompressive strength using GRILAMID TR60 is relatively low in comparisonto Examples 1, 2A and 2B which use GRILAMID TR90 in accordance with thepresent invention.

Comparative Example 10

Comparative prepreg (C10) was prepared in the same manner as Example 2Awith the only difference being that Trogamid CX7323 was used in place ofTR90 to make polyamide particles. Trogamid CX7323 contains the samepolyamide as TR90, except that both R₁ in the amine component arehydrogen instead of methyl.

The cured comparative prepreg (C10) was subjected to the same testing asin Examples 1 and 2. The CAI was only 49.6, which is relatively low incomparison to Example 2A. The G1c and G2c values were 2.2 and 7.5,respectively. The 0° compressive strength was 279 at room temperatureunder dry conditions and dropped to 185 when measured at 180° C. underwet conditions. The CAI is much lower when Trogamid CX7323 is used inplace of GRILAMID TR90 even when the polyamide particle componentcontains as little as 43 weight percent GRILAMID TR90. It is expectedthat the CAI will also be much lower when Trogamid CX7323 is used inplace of larger relative amounts of TR90 in the polyamide particlecomponent.

Having thus described exemplary embodiments of the present invention, itshould be noted by those skilled in the art that the within disclosuresare exemplary only and that various other alternatives, adaptations andmodifications may be made within the scope of the present invention.Accordingly, the present invention is not limited by the above-describedembodiments, but is only limited by the following claims.

What is claimed is:
 1. A pre-impregnated composite material comprising:A) carbon fibers; and B) a matrix resin impregnated into said carbonfibers, said matrix resin comprising: a) a resin component comprisingfrom 20 wt % to 25 wt % bisphenol-F diglycidyl ether, based on the totalweight of said matrix resin, and from 20 wt % to 25 wt %triglycidyl-p-aminophenol, based on the total weight of said matrixresin; b) a thermoplastic particle component comprising at least 95 wt%, based on the weight of said thermoplastic particle component,thermoplastic particles that comprise at least 95 wt % of a polyamidewhich is the polymeric condensation product of 1,10-decane dicarboxylicacid and an amine component having the formula

Where both R₂ are hydrogen and both R₁ are methyl and wherein saidthermoplastic particle component is present in an amount of from 10 wt %to 15 wt %, based on the total weight of said matrix resin; d) from 10wt % to 26 wt % polyether sulphone, based on the total weight of saidmatrix resin; and e) from 17 wt % to 22 wt % diaminodiphenylsulphone asa curing agent, based on the total weight of said matrix resin whereinsaid pre-impregnated composite material, when cured, has a compressionafter impact of over 60 when tested in accordance with BSS7260 per BMS8-276.
 2. The pre-impregnated composite material according to claim 1wherein said curing agent is 3,3′-diaminodiphenyl sulphone.
 3. Acomposite part comprising a pre-impregnated composite material accordingto claim 1 which has been cured.
 4. The composite part according toclaim 3 for which compression after impact is at least 60 and the wetcompression strength at 180° F. is at least
 180. 5. A The composite partaccording to claim 3 wherein said composite part forms at least part ofan aircraft primary structure.
 6. The method for making a composite partcomprising the step of curing a pre-impregnated composite materialaccording to claim 1 in order to make said composite part.
 7. The methodfor making a composite part according to claim 6 wherein the compressionafter impact of said composite part is at least 60 and the wetcompression strength of said composite part at 180° F. is at least 180.8. The method for making a composite part according to claim 6 whereinsaid composite part forms at least part of an aircraft primarystructure.
 9. The pre-impregnated composite material according to claim1 wherein the amount of said bisphenol-F diglycidyl ether in said resinmatrix is equal to the amount of said triglycidyl-p-aminophenol in saidresin matrix.
 10. The pre-impregnated composite material according toclaim 1 wherein said thermoplastic particle component consists of saidthermoplastic particles.
 11. The pre-impregnated composite materialaccording to claim 1 wherein said thermoplastic particle componentconsists of said thermoplastic particles.
 12. The pre-impregnatedcomposite material according to claim 1 wherein the amount of polyethersulphone present in said matrix resin is from 20 wt % to 26 wt %, basedon the total weight of said matrix resin.
 13. The pre-impregnatedcomposite material according to claim 12 wherein the amount of saidthermoplastic particles present in said matrix resin is 12 wt %, basedon the total weight of said matrix resin.
 14. The pre-impregnatedcomposite material according to claim 13 the amount of polyethersulphone present in said matrix resin is 23 wt %, based on the totalweight of said matrix resin.
 15. A method for making a pre-impregnatedcomposite material, said method comprising the steps of: A) providingcarbon fibers; and B) impregnating said carbon fibers with a matrixresin wherein said matrix resin comprises: a) a resin componentcomprising from 20 wt % to 25 wt % bisphenol-F diglycidyl ether, basedon the total weight of said matrix resin, and from 20 wt % to 25 wt %triglycidyl-p-aminophenol, based on the total weight of said matrixresin; b) a thermoplastic particle component comprising at least 95 wt%, based on the weight of said thermoplastic particle component,thermoplastic particles that comprise at least 95 wt % of a polyamidewhich is the polymeric condensation product of 1,10-decane dicarboxylicacid and an amine component having the formula

where both R₂ are hydrogen and both R₁ are methyl and wherein saidthermoplastic particle component is present in an amount of from 10 wt %to 15 wt %, based on the total weight of said matrix resin; d) from 10wt % to 26 wt % polyether sulphone, based on the total weight of saidmatrix resin; and e) from 17 wt % to 22 wt % diaminodiphenylsulphone asa curing agent, based on the total weight of said matrix resin, whereinsaid pre-impregnated composite material, when cured, has a compressionafter impact of over 60 when tested in accordance with BSS7260 per BMS8-276.
 16. The method for making a pre-impregnated composite materialaccording to claim 15 wherein the amount of said bisphenol-F diglycidylether in said resin matrix is equal to the amount of saidtriglycidyl-p-aminophenol in said resin matrix.
 17. The method formaking a pre-impregnated composite material according to claim 16wherein said thermoplastic particle component consists of saidthermoplastic particles.
 18. The method of making a pre-impregnatedcomposite material according to claim 15 wherein the amount of polyethersulphone present in said matrix resin is from 20 wt % to 26 wt %, basedon the total weight of said matrix resin.
 19. The method of making apre-impregnated composite material according to claim 18 wherein theamount of said thermoplastic particles present in said matrix resin is12 wt %, based on the total weight of said matrix resin.
 20. The methodof making a pre-impregnated composite material according to claim 19 theamount of polyether sulphone present in said matrix resin is from 23 wt%, based on the total weight of said matrix resin.